The present invention relates to a cutting device employing torsion.
Most mechanics, professional installers and even xe2x80x9cdo it yourselfer""sxe2x80x9d have come across the need to cut metal stock or PVC pipe. It is not uncommon that when installing a typical suspended ceiling, the metal tracks which support the ceiling tile must be cut. Even physicians employ cutting devices when sizing metal tubes and the like, for implant into the human body. In these situations, there is a strong desire to find that xe2x80x9cperfect toolxe2x80x9d which will handle the cutting in a simple, fast and economic way.
Cutting devices are well known in the art and range in complexity from the very simple to extremely elaborate. They are used in a variety of applications including the medical, construction, plumbing and electrical fields. Scissors are an example of a simple cutting device and include any device wherein a pair of rods rotate around a fixed pivot point. At one end of the rods are the handles that are closed together while at the other end are the blades which accomplish the cutting. Generally, material is placed between the blades of the scissors, at least one of which has been sharpened to a cutting edge and is offset from the other. The blades are then closed together using the handles, shearing the material. Well known in the art is the fact that shearing requires some amount of gap between the cutting edges, otherwise, the shear force necessary would render the cutting device practically useless. A severe disadvantage of the necessary xe2x80x9cgapxe2x80x9d is the burring which results on the cut edge as well as possible sources of material which could foul the cutting device. Further complicating the structure and operation of the cutting devices of the prior art is the fact that generally, in order to perform the cut, a rotational bearing is required which necessitates a housing feature. Examples of this type of cutting device is found in the disclosure of U.S. Pat. Nos. 5,261,303, 4,958,434, 3,494,233 and 2,638,985.
Unlike the afore-referenced prior art, the present invention utilizes a rotary torsion mechanism to achieve the requisite mechanical force. One of the advantages of using a twisting or torsional force to achieve a cut is the amount of force required, unlike the shear mechanism in a pair of scissors, is substantially reduced. Material to be cut is positioned in the rotary torsion cutting apparatus of the present invention so that its sectional inertial center coincides with the rotational axis. The torsion cutting force of the present invention is approximately 7.25 times more powerful than the shear force generated in connection with typical shear cutting devices.
Further, unlike the prior art, there is a zero gap between the cutting edges of the present invention. This xe2x80x9czero gapxe2x80x9d feature eliminates burring, prevents fouling, eliminates the need for a housing (consequently any bearing feature) and in all cases except for hollow round material, eliminates the need for any off-set.
It is the object of this invention to provide a simple, effective and inexpensive way to cut materials such as metal as well as PVC and copper pipe.
It is a further an object of this invention to provide a burr free cut.
Unlike the prior art which disclose shear type mechanisms, the present invention relates to a unique torsional cutting apparatus. Two plates, referred to as a stationary and rotating plate member, are positioned and held in place next to each other using any conventional means such as spring tensioned bolts such that there is a zero gap between the two plate members. The bolts are positioned through the rotating plate member and fastened to the corresponding threaded holes located on the stationary plate member. To allow rotation, the bolt holes on the rotating plate member have been elongated. The size and location of the elongated bolt holes determine both the point at which rotation begins as well as the point at which rotation stops. Further, the start position serves to align the two plates.
A fenestration or opening in the general shape of the object to be cut is fashioned through the two plate members so that the object to be cut can be placed into and through the opening. Although tapering of the opening is not required, the opening in the preferred embodiment of the present invention is tapered towards the center of the rotary torsion cutting apparatus thereby allowing ease of insertion, a more precise cut, the elimination of burring and a more defined cutting edge should the need for periodic sharpening arise. While any amount of tapering could be employed, it has been found that tapering of between 0.025 inches and 0.035 inches is the best while 0.031 inches is the preferred.
The torsional cutting apparatus of the present invention employs a torsion severance method, meaning, the opening and consequently, the object to be cut are located in the apparatus such that its inertial center coincides with the rotational axis of such apparatus thereby eliminating the need for any offset between the two plate members. Only in the instance where the object being cut is circular will any offset be required and in such case only such offset as necessary to generate sufficient cutting action is required. In cases where a hollow object is to be cut, a solid insert can be placed into such object prior to cutting to eliminate deflection and deformation of the object walls. Use of a torsional cutting force increases the amount of force generated to approximately 7.25 times that force which is generated with traditional shear devices.
Any means of causing the rotating plate member to rotate can be used, however, in the present invention, a handle attached to such plate member is employed. The handle is turned causing the rotating plate member to rotate around the inertial center of the object being cut. The handle must be rotated sufficient to achieve the desired cut, which in the preferred embodiment has been found to have been at least 90 degrees. While the type as well as number of bolts may be varied to fit particular circumstances, the present invention uses three spring tensioned bolts, placed through holes on the rotating plate member into corresponding holes located on the stationary plate member and tightened. Although the specific size and shape of the bolt holes can be changed, the size and shape of such holes of the present invention are such that the bolts may only be rotated 90 degrees.